Glycolipids such as sophorolipids (SL) are environmentally friendly and renewable biosurfactants used in detergents and other consumer and industrial products. Sophorolipids are amphiphilic molecules comprising a disaccharide of glucose in the form of sophorose, attached to a fatty acyl moiety, which can be either in the free acidic form, or in the cyclic lactone form (See, FIG. 2). Starmerella bombicola ATCC 22214, an ascomycetous yeast which has been thoroughly studied for SL production [1-3], synthesizes a mixture of several structurally related SL molecules, where the sophorose moiety is linked to the fatty acyl chain in the ω-1 carbon. SL from ascomycetous yeast Starmerella bombicola is commercially produced and utilized in consumer and industrial products, but commercialization is limited to high-end products due to high production costs.
SL synthesis by fermentation with yeast species Starmerella bombicola requires both a carbohydrate and a hydrophobic substrate such as a purified fatty acid or vegetable oil [4]. SL secretion is less than one g/L when fed 100 g/L glucose with no hydrophobic substrate [5]. Higher yields require energetically costly and expensive substrates, such as oleic acid or canola oil. Therefore, the S. bombicola process is only economically viable for relatively high value products such as detergents and emulsifiers.
Fourteen yeast species have been reported to produce and secrete glycolipids known as sophorolipids (SL) in industrially relevant amounts (at least 1 g/L, see Table 1):
TABLE 1Yeast Species Reported To Produce And SecreteCommercially Relevant Amounts Of SophorolipidsSpeciesYear of publicationReferenceCandida albicans2012 [6]Candida apicola1961[7, 8](syn. Torulopsis magnoliae)Candida batistae2008 [9]Candida florícola2010[10]Candida gropengiesseri1967[11](syn. Torulopsis gropengiesseri)Candida kuoi2010[12, 13]Candida riodocensis2010[12]Candida stellata2010[12]Cyberlindnera samutprakarnensis2013[14]Rhodotorula bogoriensis1968[15]Starmerella bombicola1970[16-19](syn. Candida bombicola)Wickerhamiella domercqiae2006[20]Wickerhamomyces anomalus2008[21](syn. Pichia anomala)Yarrowia lipolytica1984[22](syn. Torulopsis petrophilum)
All of the previously known SL producing yeasts belong to the phylum Ascomycota except one: Pseudohyphozyma bogoriensis, (syn. Rhodotorula bogoriensis), a yeast belonging to the phylum Basidiomycota, class Microbotryomycetes, in an unclassified clade that includes R. buffonii and R. pustula [23-25]. This species is not in the order Sporidiobolales. All SL producing yeasts previously known require provision of both a carbohydrate such as glucose, and a hydrophobic substrate such as vegetable oil, fatty acids, alkanes or tryacylglycerols in order to produce commercially useful quantities of glycolipids. U.S. Pat. Nos. 3,205,150 and 3,312,684 describe production of glycolipids (referred to in both patents as glycosides of hydroxyl fatty acids) via a fermentation process using the osmophilic yeast Torulopsis magnonliae (syn. Candida apicola), an ascomycete yeast species, where a carbohydrate and a nitrogen source is added to the culture to enhance yeast growth, and then a hydrophobic substrate is added to promote production of such compounds. U.S. Pat. No. 4,297,340 uses C. bombicola (syn. Starmerella bombicola), another ascomycete yeast, and beef tallow as a hydrophobic substrate using a similar method to produce glycolipids which were further derivatized as glycolipid esters to create improved moisturizers for cosmetic purposes. U.S. Pat. No. 5,616,479 uses S. bombicola and improved prior art by including fed-batch additions of esters of oils and fatty acids, and recovering the product by settling and water washing, during controlled intervals where agitation and aeration are stopped. More recent patents using glycolipids from S. bombicola as microbial protein inducer still undergo the same production method using hydrophobic substrates to create glycolipids (see Intl. Publ. No. WO 2007/073371 A1). The main disadvantage of the previous art is that it requires dosing of hydrophobic substrates during the fermentation, increasing the cost and adding complexity to the recovery of the product.